Crash test dummies are used in the automotive industry for practical testing of the driving safety of vehicles. A large number of different standardized tests are required for the approval of new vehicles. These tests provide for a frontal crash without offset, frontal crashing with partial offset, side crashing, and the like. The tests are carried out with the vehicle for which approval is being sought using at least one crash test dummy that is sitting therein. Crash test dummies simulate human beings during the tests and use a complex sensor system to record the influences of the impact acting on them. For instance, acceleration sensors are commonly placed at numerous points, such as in the head and chest. Moreover, force sensors are often used which measure the profiles of the forces acting on individual body parts, such as the knee, abdomen, thorax, cervical spine, and the like.
One of the critical factors that poses a health hazard during a collision is chest intrusion during the impact. Crash test dummies are equipped with artificial ribs that simulate human rib cages. The intrusion of human ribs can be so extreme in a side impact, for example, that ribs break, which can pose a danger for the underlying organs in some circumstances. In order to measure intrusions in such crash tests, displacement transducer arrangements are known in the prior art that are arranged on the spinal column of the crash test dummy on the one hand and on the rib cage on the other.
A great number of requirements are placed on the displacement transducer arrangements. They must be able to measure the distances precisely but also sufficiently quickly in order to detect the dynamics of the intrusion, since they, in addition to the absolute values, have a substantial influence on the human occupants' risk of injury. The displacement transducer arrangements must be able to perform measurements at up to 18 m/s.
One known displacement transducer arrangement, which is explained in conjunction with FIG. 7, provides for an arrangement of sleeves that can be displaced relative to one another between a first mounting on the spinal column and a second mounting on the rib cage. A light source, such as an IR LED, for example, is provided in the interior of the sleeve arrangement that emits to a sensor that is provided on the other mounting. The amount of light that arrives at the sensor determines the distance between light source and sensor, so that the luminance is a measure of distance. The use of this arrangement requires that a power supply be provided on both mountings, which is achieved in the prior art by means of a cable that is routed outside of the sleeves. This cable can be easily damaged, which renders the displacement transducer arrangement useless. What is more, the mutually displaceable sleeves can be displaced haphazardly relative to one another as a result of a change of distance caused by an intrusion, which results in a haphazard sleeve configuration at a given distance between the two mountings. This causes variances in the measured light signal, since the sleeve walls are light-reflective, and the sum of all light paths for different sleeve configurations result in different brightnesses at the receiver. In addition, light sources and sensors require a relatively high amount of energy, so that a comparatively high-energy power supply is needed. The supply voltage is 5 V, whereas conventional instrumentation amplifiers in crash test dummies operate at 2.5 V to 3.3 V. Special solutions are therefore required for the power supply. The residual heat of the instrumentation amplifier and of the light slowly heats up the displacement transducer arrangement and the crash test dummy, which has an impact on the dark current of the sensor. The measurement accuracy thus depends on the temperature of the displacement transducer arrangement. Furthermore, the temperature of the crash test dummy is defined during the measurement. What is more, the calibration of such displacement transducer arrangements is difficult due to the abovementioned circumstances. The sensor also delivers a nonlinear voltage signal that must be subsequently linearized. To achieve this, the zero position of the sensor must be known. The measurement accuracy increases as a result of the subsequent linearization. What is more, the signal-to-noise ratio becomes unfavorable at large distances to the light source.
Moreover, displacement transducer arrangements are known that work with string potentiometers. These have low limits in terms of the speeds that can be achieved. At speeds of greater than 4 m/s, the cable can slacken, which distorts the measuring results.
Rod potentiometers are known as well, but, due to their construction, they make only half of the maximum length available as a measured distance. Its maximum travel speed is 10 m/s.